Magnetism and Spin

In recent years we have examined magnetic materials on the nanoscale as a part of our work on group of Prof. Emilia Morosan, we examined Fe\(_{x}\)TaS\(_{2}\), a material consisting of iron intercalated between 2d layers of TaS\(_{2}\). This material is known to be a very "hard", Ising-like ferromagnet below an ordering temperature that depends on \(x\). We found that when \(x=0.28\), this material exhibits a magnetoresistance approaching 100% at low temperatures, in stark contrast with the commensurate phases when \(x=1/4\) or \(1/3)\), which have magnetoresistances of more like 1%. (Bear in mind that "giant" magnetoresistance is typically a 20% effect.) This work has been published here. The comparison between bulk crystals and exfoliated pieces was important for establishing that the effects we were observing were unlikely to be associated with the micron-scale domains typical of the \(x=1/4\) material.

Similarly, in collaboration with Prof. Jun Lou's group, we have used transport to examine the thickness dependence of antiferromagnetism in V5S8, and in the course of those experiments we discovered a previously unknown metamagnetic phase transition between the antiferromagnetic phase and a paramagnetic phase. That transition extrapolates to a quantum phase transition at \(T = 0\) and around 19 Tesla.

We are also very interested in the transport of spin in nanostructures. We are planning and performing experiments using shot noise spectroscopy to look at the accumulation of spin driven by the spin Hall effect. Moreover, we are planning and performing experiments to understand the quantum spin Hall effect that arises in certain topologically nontrivial semiconductor interfaces and some single-layer 2d materials. Specifically, we will be using noise spectroscopy to understand the nature of edge transport in such systems.